Nuclear Theory·nucl-th

Tuesday·January 10, 2017

14 papers—7 primary·7 cross-listed

01
Revisit of directed flow in relativistic heavy-ion collisions from a multiphase transport model
Chong-Qiang Guo🇨🇳 · Chun-Jian Zhang🇨🇳 · Jun Xu🇨🇳
We have revisited several interesting questions on how the rapidity-odd directed flow is developed in relativistic $^{197}$ Au+ $^{197}$ Au collisions at $s_{N N}$ = 200 and 39 GeV based on a multiphase transport model. As the partonic phase evolves with time, the slope of the parton directed flow at midrapidity region changes from negative to positive as a result of the later dynamics at 200 GeV, while it remains negative at 39 GeV due to the shorter life time of the partonic phase. The directed flow splitting for various quark species due to their different initial eccentricities is observed at 39 GeV, while the splitting is very small at 200 GeV. From a dynamical coalescence algorithm with Wigner functions, we found that the directed flow of hadrons is a result of competition between the coalescence in momentum and coordinate space as well as further modifications by the hadronic rescatterings.
nucl-thhep-exnucl-exEPJA(2017)·15 citations
02
Analytical coalescence formula for particle production in relativistic heavy-ion collisions
Kai-Jia Sun🇨🇳 · Lie-Wen Chen🇨🇳
Based on a covariant coalescence model with a blast-wave-like parametrization for the phase-space configuration of constituent particles at freeze-out, we derive an approximate analytical formula for the yields of clusters produced in relativistic heavy-ion collisions. Compared to previous existing formulae, the present work additionally considers the contributions from the longitudinal dimension in momentum space, the relativistic corrections and the finite size effects of the produced clusters relative to the spatial distribution of constituent particles at freeze-out. The new analytical coalescence formula provides a useful tool to evaluate the yield of produced clusters, such as light nuclei from nucleon coalescence and hadrons from quark coalescence, in heavy-ion collisions. As a first application of the new analytical formula, we explore the strangeness population factor $S_{3} =_{Λ}^{3}$ H/( $^{3}$ He $\times Λ/$ p) based on nucleon/ $Λ$ coalescence as well as the production of exotic hadrons based on quark coalescence, in central Pb+Pb collisions at $s_{N N} = 2.76$ TeV. The results are compared with the predictions from other models.
nucl-thastro-ph.HEhep-phnucl-exPRC(2017)·58 citations
03
Microscopic dynamics simulations of multi-nucleon transfer in $^{86}$ Kr+ $^{64}$ Ni at 25 MeV/nucleon
Hong Yao · Ning Wang
Multi-nucleon transfer in $^{86}$ Kr+ $^{64}$ Ni at an incident energy of 25 MeV/nucleon is for the first time investigated with a microscopic dynamics model: improved quantum molecular dynamics (ImQMD) model. The measured isotope distributions are reasonably well reproduced by using the ImQMD model together with a statistical code (GEMINI) for describing the secondary decay of fragments. The reaction mechanism is explored with the microscopic dynamics simulations from central to peripheral collisions. In central collisions there exists a strong competition among fusion, deep-inelastic scattering and multi-fragmentation at such an incident energy. In semi-peripheral collisions, binary scattering together with nucleon transfer is dominant, and the probability of elastic+inelastic scattering events increases rapidly with impact parameter in peripheral collisions and approaches to one when $b > 14$ fm. The mass-TKE distribution in central collisions due to the competition is quite different from those in peripheral collisions and the distribution of total kinetic energy loss (TKEL) for binary events with nucleon transfer is much more broader than those without transfer.
nucl-thPRC(2017)·23 citations
04
Observables for longitudinal flow correlations in heavy-ion collisions
Jiangyong Jia🇺🇸 · Peng Huo🇺🇸 · Guoliang Ma🇨🇳 · Maowu Nie🇺🇸
We propose several new observables/correlators, based on correlations between two or more subevents separated in pseudorapidity $η$ , to study the longitudinal flow fluctuations. We show that these observables are sensitive to the event-by-event fluctuations, as a function of $η$ , of the initial condition as well as the non-linear mode-mixing effects. Experimental measurement of these observables shall provide important new constraints on the boost-variant event-by-event initial conditions required by all 3+1-dimensional viscous hydrodynamics models.
nucl-thnucl-exJ.Phys.G(2017)·33 citations
05
Production of $Λ_{c}^{+}$ hypernuclei in antiproton - nucleus collisions
R. Shyam🇮🇳 · K. Tsushima🇧🇷
We investigate the production of charm-baryon hypernucleus $_{Λ_{c}^{+}}^{16}$ O in the antiproton - $^{16}$ O collisions within a fully covariant model that is based on an effective Lagrangian approach. The explicit $Λ ˉ_{c}^{-} Λ_{c}^{+}$ production vertex is described by the $t$ -channel $D^{0}$ and $D^{* 0}$ meson-exchanges in the initial collision of the incident antiproton with one of the protons of the target nucleus. The $Λ_{c}^{+}$ bound state spinors as well as the self-energies of the exchanged mesons employed in our calculations are derived from the quark-meson coupling model. The parameters of various vertices are taken to be the same as those used in our previous study of the elementary $p ˉ + p \to Λ ˉ_{c}^{-} + Λ_{c}^{+}$ reaction. We find that for antiproton beam momenta of interest to the $P ˉ A N D A$ experiment, the 0 $^{\circ}$ differential cross sections for the formation of $_{Λ_{c}^{+}}^{16}$ O hypernuclear states with simple particle-hole configurations, have magnitudes in the range of a few $μ$ b/sr.
nucl-thhep-exhep-phnucl-exPLB(2017)·21 citations
06
Charmonium spectrum and diffractive production in a light-front Hamiltonian approach
Guangyao Chen🇺🇸 · Yang Li🇺🇸 · Pieter Maris🇺🇸 · Kirill Tuchin🇺🇸 · James P. Vary🇺🇸
We study exclusive charmonium production in diffractive deep inelastic scattering and ultra-peripheral heavy-ion collisions within the dipole picture. The mass spectrum and light-front wavefunctions of charmonium are obtained from the basis light-front quantization approach, using the one-gluon exchange interaction plus a confining potential inspired by light-front holography. We apply these light-front wavefunctions to exclusive charmonium production. The resulting cross sections are in reasonable agreement with electron-proton collision data at HERA and ultra-peripheral nucleus collision measurements at RHIC and LHC. The charmonium cross-section has model dependence on the dipole model. We observe that the cross-section ratio of excited states to the ground state has a weaker dependence than the cross-section itself. We suggest that measurements of excited states of heavy quarkonium production in future electron-ion collision experiments will impose rigorous constraints on heavy quarkonium light-front wavefunctions, thus improving our understanding of meson structure, which eventually will help us develop a precise description of the gluon distribution function in the small- $x$ regime.
nucl-thNucl.Part.Phys.Proc.(2017)·2 citations
07
Statistical model analysis of $α$ -induced reaction cross sections of $^{64}$ Zn at low energies
P. Mohr · Gy. Gyürky · Zs. Fülöp
Background $α$ -nucleus potentials play an essential role for the calculation of $α$ -induced reaction cross sections at low energies in the statistical model. Uncertainties of these calculations are related to ambiguities in the adjustment of the potential parameters to experimental elastic scattering angular distributions (typically at higher energies) and to the energy dependence of the effective $α$ -nucleus potentials. Purpose The present work studies cross sections of $α$ -induced reactions for $^{64}$ Zn at low energies and their dependence on the chosen input parameters of the statistical model calculations. The new experimental data from the recent Atomki experiments allow for a $χ^{2}$ -based estimate of the uncertainties of calculated cross sections at very low energies. Method The recent data for the ( $α$ , $γ$ ), ( $α$ , $n$ ), and ( $α$ , $p$ ) reactions on $^{64}$ Zn are compared to calculations in the statistical model. A survey of the parameter space of the widely used computer code TALYS is given, and the properties of the obtained $χ^{2}$ landscape are discussed. Results The best fit to the experimental data at low energies shows $χ^{2} / F \approx 7.7$ per data point which corresponds to an average deviation of about 30% between the best fit and the experimental data. Several combinations of the various ingredients of the statistical model are able to reach a reasonably small $χ^{2} / F$ , not exceeding the best-fit result by more than a factor of 2. Conclusions The present experimental data for $^{64}$ Zn in combination with the statistical model calculations allow to constrain the astrophysical reaction rate within about a factor of 2. However, the significant excess of $χ^{2} / F$ of the best-fit from unity asks for further improvement of the statistical model calculations and in particular the $α$ -nucleus potential.
nucl-thnucl-exPRC(2017)·16 citations
08
The hidden-charm multiquark states
Hua-Xing Chen🇨🇳 · Wei Chen🇨🇦 · Jun He🇨🇳 · Xiang Liu🇨🇳 · Shi-Lin Zhu🇨🇳
Since 2003 many charmonium-like states were observed experimentally. Especially those charged charmonium-like $Z_{c}$ states and bottomonium-like $Z_{b}$ states cannot be accommodated within the naive quark model, which are good candidates of either the hidden-charm tetraquark states or molecules composed of a pair of charmed mesons. In 2015, the LHCb Collaboration discovered two hidden-charm pentaquark states, which are also beyond the quark model. In this talk, we review the current experimental progress and investigate various theoretical interpretations of these candidates of the multiquark states. We list the puzzles and theoretical challenges of these models when confronted with the experimental data. We also discuss possible future measurements which may distinguish the theoretical schemes on the underlying structures of the hidden-charm multiquark states.
↳ hep-phhep-exhep-latnucl-thPoS(2017)·1 citation
09
Proton rms-radii from low-q power expansions?
Ingo Sick🇨🇭 · Dirk Trautmann🇨🇭
Several recent publications claim that the proton charge {\em rms}-radius resulting from the analysis of electron scattering data restricted to {\em low} momentum transfer agrees with the radius determined from muonic hydrogen, in contrast to the radius resulting from analyses of the full (e,e) data set which is $0.04 f m$ larger. Here we show why these publications erroneously arrive at the low radii.
↳ nucl-exnucl-thPRC(2017)·26 citations
10
$ϕϕ$ and $J / ψ ϕ$ mass spectra in decay $B_{s}^{0} \to J / ψ ϕϕ$
A.A. Kozhevnikov🇷🇺
The mass spectra of the $ϕϕ$ and $J / ψ ϕ$ states in the decay $B_{s}^{0} \to J / ψ ϕϕ$ recently observed by LHCb are calculated in the model which takes into account the $J^{P} = 0^{+}, 0^{-}, 2^{+}$ intermediate resonances $R_{1}$ , $R_{2}$ in the $ϕϕ$ channel and the $J^{P} = 1^{+}$ ones, $X_{1}$ , $X_{2}$ , in the $J / ψ ϕ$ channel. When obtaining the expressions for the effective amplitudes and mass spectra, the approximate threshold kinematics of the decay is used essentially. The $R_{1} - R_{2}$ and $X_{1} - X_{2}$ mixings arising due to the common decay modes $ϕϕ$ and $J / ψ ϕ$ , respectively, are also taken into account. The obtained expressions for the mass spectra are applied for extracting the information about masses and coupling constants of the resonances in the $ϕϕ$ and $J / ψ ϕ$ final states.
↳ hep-phhep-exnucl-thPRD(2017)·2 citations
11
Spin-dependent sum rules connecting real and virtual Compton scattering verified
Vadim Lensky🇩🇪 · Vladimir Pascalutsa🇩🇪 · Marc Vanderhaeghen🇩🇪 · Chung Wen Kao🇹🇼
We present a detailed derivation of the two sum rules relating the spin polarizabilities measured in real, virtual, and doubly-virtual Compton scattering. For example, the polarizability $δ_{L T}$ , accessed in inclusive electron scattering, is related to the spin polarizability $γ_{E 1 E 1}$ and the slope of generalized polarizabilities $P^{(M 1, M 1) 1} - P^{(L 1, L 1) 1}$ , measured in, respectively, the real and the virtual Compton scattering. We verify these sum rules in different variants of chiral perturbation theory, discuss their empirical verification for the proton, and prospect their use in studies of the nucleon spin structure.
↳ hep-phnucl-exnucl-thPRD(2017)·14 citations
12
Search for the QCD Critical Point with Fluctuations of Conserved Quantities in Relativistic Heavy-Ion Collisions at RHIC : An Overview
Xiaofeng Luo🇨🇳 · Nu Xu🇨🇳
Fluctuations of conserved quantities, such as baryon, electric charge and strangeness number, are sensitive observables in relativistic heavy-ion collisions to probe the QCD phase transition and search for the QCD critical point. In this paper, we review the experimental measurements of the cumulants (up to fourth order) of event-by-event net-proton (proxy for net-baryon), net-charge and net-kaon (proxy for net-strangeness) multiplicity distributions in Au+Au collisions at $s_{N N} = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, 200$ GeV from the first phase of beam energy scan program at the Relativistic Heavy-Ion Collider (RHIC). We also summarize the data analysis methods of suppressing the volume fluctuations, auto-correlations and the unified description of efficiency correction and error estimation. Based on theoretical and model calculations, we will discuss the characteristic signatures of critical point as well as backgrounds for the fluctuation observables in heavy-ion collisions. The physics implications and the future second phase of the beam energy scan (2019-2020) at RHIC will be also discussed.
↳ nucl-exhep-exhep-phnucl-thNucl.Sci.Tech.(2017)·550 citations
13
Strong isospin breaking at production of light scalars
N.N. Achasov🇷🇺 · G.N. Shestakov🇷🇺
It is discussed breaking the isotopic symmetry as the tool of studying the mechanism production and nature of light scalar mesons.
↳ hep-phhep-exnucl-thNucl.Part.Phys.Proc.(2017)·9 citations
14
Temperature dependence of shear viscosity of $S U (3)$ --gluodynamics within lattice simulation
Nikita Astrakhantsev🇷🇺 · Viktor Braguta🇷🇺 · Andrey Kotov🇷🇺
In this paper we study the shear viscosity temperature dependence of $S U (3)$ --gluodynamics within lattice simulation. To do so, we measure the correlation functions of energy-momentum tensor in the range of temperatures $T / T_{c} \in [0.9, 1.5]$ . To extract the values of shear viscosity we used two approaches. The first one is to fit the lattice data with some physically motivated ansatz for the spectral function with unknown parameters and then determine shear viscosity. The second approach is to apply the Backus-Gilbert method which allows to extract shear viscosity from the lattice data nonparametrically. The results obtained within both approaches agree with each other. Our results allow us to conclude that within the temperature range $T / T_{c} \in [0.9, 1.5]$ SU(3)--gluodynamics reveals the properties of a strongly interacting system, which cannot be described perturbatively, and has the ratio $η / s$ close to the value $1 / 4 π$ in $N = 4$ Supersymmetric Yang-Mills theory.
↳ hep-lathep-phhep-thnucl-thJHEP(2017)·108 citations

Affiliations

first authorsco-authorsvia INSPIRE